Implantable hearing aids stimulate internal components of the auditory system and are generally classified into one of two types, namely semi-implantable hearing aids and fully implantable hearing aids. In a semi-implantable hearing aid, some of the components, typically the microphone, power supply, and speech signal processor, are externally worn, while the transducer and key support functions are implanted within the auditory system. The externally worn portion and the implanted portion communicate transcutaneously to provide audio sound to the auditory system. In a fully implantable hearing aid, the entire device including the power supply, speech processor, microphone, and transducer are implanted subcutaneously.
Implanted hearing aids are typically used by individuals with significant loss of hearing function or damage to the auditory system. As a result, they differ in the manner by which the signal is processed and delivered to the patient. The processing step, known in the art as Speech Signal Processing (“SSP”), may include a number of steps such as amplification, frequency shaping, compression, etc. The steps in the SSP are determined by the design of the hearing aid, while the particular internal values used in the steps are generated from prescriptive parameters determined by an audiologist. Once a speech processor processes ambient acoustic signal, the altered signal is provided to an implanted transducer that stimulates the hearing impaired person's auditory system. The auditory stimulation may be done acoustically, mechanically, or electrically as a function of the type and severity of the hearing loss in the hearing impaired individual.
The Speech Signal Processing (SSP) may include a number of steps that are determined by the design of the hearing aid, while the particular internal values or fitting parameters used in the steps are generated from prescriptive parameters (PP) determined by the audiologist. For instance, the number of frequency bands used by a hearing aid are determined by the design, while the desired amount of attenuation of each frequency band is given as a prescriptive parameter, and the actual numbers used in the hearing aid to set these frequency attenuations are the internal values/fitting parameters.
In adapting a given hearing aid to a given patient, the various PP must be chosen to provide the most benefit to the patient, and are typically determined by a process known as fitting. This fitting process comprises determining various measures of the patient's hearing perception, generating the desired compensation as PP via a fitting algorithm, or simply algorithm. Continuing the fitting process, the PP are then converted to fitting parameters for the hearing aid, the hearing aid is programmed with these fitting parameters and then verifying that these fitting parameters demonstrably correspond to the desired PP. Once this is completed, the hearing aid is operated and various measures of the patient's aided hearing perception are determined to find out if the fitting process has been successful. If the patient's aided hearing perception is within acceptable limits the fitting is completed. Otherwise, the audiologist may elect to alter either the PP or the fitting parameters from the prescribed values slightly in order to attempt to improve the results for the patient.
The patient's hearing perception may be measured by subjecting the patient to various sound test protocols well known to those skilled in the art. These test protocols consist of sounds presented to the patient via speakers or headphones or in the case of implanted devices by direct application of an audio drive signal to an implanted transducer. The sounds may consist of tones, composite tones, multiple tones, speech, or the like, and they may be presented to one or both of the ears. For example, a common measurement of a patient's hearing perception is to subject the patient to a sequence of pure tones at specific “audiometric” frequencies. A device known as an audiometer is typically used to generate this sequence of tones as electrical signals which are thence conducted by a cable to the speakers or headphones. These tones are presented to the subject at various amplitudes according to specific protocols used in the industry.
Once the appropriate audiometric measures are performed, a fitting algorithm is used to convert this data into the most appropriate mapping between the patient's hearing and normal hearing. This process is not as simple as it sounds as various schools of thought exist as to the best fitting algorithms, and the range of their applicability. The results of the algorithm is a set of mapping parameters describing how to map the acoustic input into the patient's perception as prescriptive parameters. Typically, calculations of the algorithm are computationally complex resulting in significant waiting times during fitting.
Once this is done, the prescriptive parameters must be converted into parameters suitable for use inside of the hearing aid. Depending on the technology used in the speech signal processing, this results in numbers, here called internal values or fitting parameters, which are then programmed into the hearing aid. This function is often included in the function of the fitting software.
After the operation of the hearing aid is confirmed, the appropriate internal values are programmed into the hearing aid, and the device is once again operated and analyzed. The expected performance of the desired program is then confirmed by comparing the actual response of the programmed device with the desired performance. This confirms that the patient will be receiving at least approximately the desired amount of hearing compensation by the aid, will not be subjected to an excessive amount of acoustic energy, and that the performance of the aid will be suitable to warrant further tests with the patient.
If, as occasionally happens, the actual response of the device as determined by the hearing aid analyzer is different from the desired response by a significant amount, the audiologist may elect to adjust the programmed internal values, or somewhat equivalently, the prescriptive parameters. This may necessitate repeating the above-noted process. Accordingly, the fitting procedure may be quite time consuming.